1. Field of the Invention
The present invention provides a media feeding apparatus. More specifically, the present invention provides a media feeding apparatus which enables feeding of media having a high coefficient of friction which are disposed against a media tray.
2. Description of the Related Art
Various mechanisms have been utilized to feed media into a printer or other peripheral. Various of these mechanisms utilize a tray or bin in order to support a stack of media in which the upper most sheet of the stack may be advanced to a processing station or printing area for printing by a laser printer or inkjet printer, for example. In typical printing or duplicating devices, individual sheets of print media are advanced from the media tray to the processing station by utilizing a paper picking device.
At least one peripheral manufacturer currently uses auto-compensating mechanism (ACM) devices to pick media from a media tray. For example, as related to printers, the L-Path (Top Load) and C-Path printers (Bottom Load) both use the ACM to separate one sheet of paper from the paper stack to feed into the print zone. The ACM is effective because it generates more normal (downward) force as the resistance to moving the paper increases. This keeps the pick tires from slipping as resistance increases. For example, stiff photo paper might have many times the resistance to picking as plain paper. Part of the optimization of the ACM device depends on the friction between each sheet in the stack which is assumed to be similar between each sheet in the stack and within a certain predetermined range. This however leads to a common problem with the design in picking the last sheet. The media trays are typical made of some type of hard plastic that does not have friction similar to that of the media. When the media to plastic friction is too low the last few sheets may be picked together rather than individually, which leads to multi-sheet feeds and paper jams.
Several designs have been made in an attempt to overcome this problem. For example, a soft foam pad may be disposed in the media tray that provides equal or greater friction than the sheet-to-sheet friction so that the last sheet is held in place when the feedingmechanism approaches the bottom of the stack. The foam pad design has been refined for a variety of paper types and used in many peripheral devices including both L-path and C-path printers. However with the advent of micro-porous photo (MPP) papers, an additional problem has manifested. The printed surfaces of MPP papers are soft and have a very high coefficient of friction. The foam pad overcomes the problem of media multi-sheet feeding. However, when feeding the last sheet of media and because the ACM generates more force as the resistance increases, it becomes a self-defeating device if the friction is too high. A polytetrafluoroethylene (PTFE) material, generally known to the public by DuPont's brand name Teflon®, has been located at a lower elevation than the pad so that the downforce of the ACM compresses the foam pad causing the media to engage the PTFE material allowing the sheet to feed. However, the cost per unit is high with the PTFE—foam pad arrangement and tolerances involved in such structure have been extremely difficult to control. For example, when the PTFE material elevation is too high, multi-sheet feeds are likely to occur. Conversely, when the Teflon is too low, pick problems previously described occur. Further, print motor stalls were common with such design rendering it unreliable.
What is needed is a media feeding mechanism that is usable with both lightweight media and heavier, thicker photo media and also inhibits multi-sheet feeds while allowing feeding of the last media sheet when normal force increases.